Method and apparatus for broaching gears



1966 A. B. STREMPEL 3,

METHOD AND APPARATUS FOR BROACHING GEARS Filed iylay 18, 1965 UnitedStates Patent O 3,293,983 METHQD AND APPARATUS EUR BRQAQHHNG GEAltEeAlfred B. Strernpel, Deep River, Conn., assignor to Giannini ControlsCorporation, Duarte, Calif, a corporation of New York Filed May 18,1965, Ser. No. 456,697 7 Claims. (Cl. 90-10) This invention has to dowith improvements in conventional systems for producing gears wherein agear blank is forcibly advanced through a series of distinct axiallyalined dies which progressively form gear teeth on the periphery of theblank.

The invention is particularly although not exclusively useful inconnection with such broaching systems in which the gear blank isadvanced by a pushing punch which accurately fits the final finishing orpolishing die, thereby producing accurately formed teeth substantiallyfree of burrs. The fundamentals of that method of operation andmechanism for carrying it out are fully described in the United StatesPatent 3,162,089, issued December 22, 1964, to Frank L. Riggio and me,as joint inventors, under the title Gear Broaching Apparatus.

One aspect of the present invention provides improved structure for thefinal die, and procedure for obtaining the desired very close fit of thepushing punch in the final die in systems of the type just described. Inaccordance with this aspect of the invention, the final die comprises athin wall annular die insert with a conically tapered outer surfacepressed into a die holder or die block with a matching tapered hole.During final fitting of the die to the pushing punch, the die can bepressed further into the die holder, thereby effectively shrinking theaperture in the die and reducing the dimensions of the die teeth in thecircumferential direction. Also, as the die wears during use, it can beresized by forcing it further into the die holder, followed by relappingif needed.

We have found that such tapered form of a die assembly is effective onlyif the included angle of taper is within the critical range betweenabout 3 and about the range between 4 and 8 being preferred.

A further aspect of the present invention is concerned more particularlywith improved mechanism for broaching or shaving gears accurately andrapidly with minimum diificulty in clearing the chips from the workingdies. A common difiiculty in forming parts by breaching or shavingresults when one die cuts all the way around the blank, thus forming aring of cut material. Such rings tend to plug up the chip space betweenthe dies, and occupy an abnormal amount of space in the chip strainer.

The present invention avoids such difiiculties from ring formationwithout requiring any increase in the number of dies or otherwisereducing the efficiency and convenience with which the desired gear formis produced.

In the production of gears of high quality it is desirable that theinitial blank have a diameter greater than the outside diameter of thefinished gear, so that material is removed all around the blank duringthe breaching or shaving process. Only in that way can the concentricityof the finished gear be defined entirely during the broaching processand thus be independent of possible eccentricity of the blank.

In forming the channels between the gear teeth, the greatest depth ofmaterial that must be removed is at the roots of the teeth. It isdesirable that all the cutting dies share significantly and preferablyapproximately uniformly in attaining that total depth of cut, so thatboth the number of dies and the maximum depth of cut by any one die maybe as small as possible.

The present invention provides such substantial uni- 3293,93 FatentedDec. 27, 1966 formly of cut by the several successive dies as well asaccurate formation of the tops of the teeth, while avoiding any tendencytoward the formation of chips of ring form.

That is accomplished by designing the first die and a subsequent cuttingdie to produce coordinated cutting action of specialized type. The firstcutting die, which initiates formation of the channels between the gearteeth, is designed to clear the periphery of the blank at the pointswhere the tops of the teeth will later be formed. A subsequent die thenforms the tops of the teeth and also deepens the channels between theteeth. However, that die, which is preferably the second one and will beso denoted for clarity of description, clears the work at the sides ofthe previously cut channel. The dead spots produced by that clearanceseparate the two areas of cut at the tops of the gear teeth and at thebottoms of the channels, positively preventing the formation of rings.

The third and subsequent cutting dies then further deepen the channelsbetween the teeth until the full desired depth to the roots of therough-cut teeth is attained. The number ofcutting dies will depend uponthe size and form of the gear and-to some extent upon the material to beused. For relatively small and fine gears, such as are used in geartrains in timing mechanisms and the like, a total of four cutting diesahead of the finishing die is generally suitable. For larger gears, asmany as eight or ten cutting dies may be used.

In preferred form of the invention, each of the cutting dies except thefirst conforms accurately to the final tooth forms at the tops of thegear teeth. Hence, when the pushing punch is designed, as described inthe above in the above identified patent, to fit accurately in thefinishing die, it will be also fit all of the cutting dies except thefirst at the roots of the cutting teeth, and will therefore beaccurately centered throughout its stroke and guided cleanly ino thefinishing die.

It is preferred, further, that the sides of the teeth of each cuttingdie except the second conform essentially to the final tooth form exceptfor a small uniform clearance which is removed by the final or finishingdie. All of the cutting dies can then be broached with the same toolsand can be finished with the same lap or laps, as will be more fullydescribed.

It may be noted that the problem of ring formation does not arise whenthe tops of the gear teeth are not formed during the breaching orshaving process but coincide with the periphery of the initial blank, asshown, for example, in FIG. 8 of Patent 2,461,320 to Lee B. Green. Asalready indicated, optimum concentricity of the finished gear requiresthat all parts of the teeth be machined with reference to the samecentering operation. Nor does the problem of ring formation arise in itspresent form when the initial blank is preformed with a scalloped edgeapproximating the desired gear teeth, as shown, for example, in Patent2,237,959 to William L. Hansen et al. The latter system entailsunacceptable expense, since it requires in addition to preforming thescalloped blank, that the blank be correctly positioned for shaving bothas to rotation and as to centering.

In accordance with a further aspect of the invention, the describedclearance between the second (or later) die and the sides of thepreviously cut channels in the blank is produced in a particularlyconvenient and accurate manner during the lapping of that die. Greateconomy is obtained by initially breaching all the cutting dies to thesame tooth form, with the die teeth initially extending the fulldistance to the roots of the gear teeth to be formed. The sides androots of the cutting teeth of the third and subsequent dies are thenlapped to the same tooth form in a manner that may be essentiallyconventional. After such lapping to the desired common tooth form, thetops of the die teeth are ground off to give the desired progressivevariation in their respective inner diameters to determine the relativedepth of cut for each of the dies. In lapping the second die the widthof the cutting teeth reduced by applying a yielding torsion, first inone direction and then in the other, to the lap. The described clearancebetween the sides of the cutting teeth and the work is thereby obtainedwithout requiring a special lap.

The same procedure of applying torsion to the lap may also be utilizedfor finishing other working parts of the present gear shaving apparatus,particularly for lapping the final die to fit the pushing punch asprecisely as possible.

A full understanding of the invention and of its further objects andadvantages will be had from the following description of certainillustrative manners in which it may be carried out. The particulars ofthat description, and of the accompanying drawings which form a part ofit, are intended only as illustration and not as a limitation upon thescope of the invention, which is defined in the appended claims.

In the drawings:

FIG. 1 is a vertical axial section representing the primary workingparts of an illustrative gear shaving machine in accordance with theinvention;

FIG. 2 is a side elevation, partly cut away, representing a final dieinsert in accordance with the invention;

FIG. 3 is a section on the line 33 of FIG. 1 at greatly enlarged scale;

FIG. 4 is a schematic side elevation representing a lapping machine inaccordance with the invention; and

FIG. 5 is a fragmentary plan corresponding to FIG. 4.

FIG. 1 shows the primary working elements of an illustrative apparatusfor shaving gears in accordance with the present invention. The pushingpunch and the shedder punch 30 are mounted for movement in a coordinatedmanner along the axis 18, as by hydraulic cylinders, not explicitlyshown, which are coupled to the outer ends of the punches in anysuitably manner. Pushing punch 20 typically comprises a smoothcylindrical shank section 21, guided in the bearing block 22 which maybe provided with a bushing 23, and a hobbed working section 24 whichconforms accurately to the shape of the finished gear and is guided inthe fitting punch guide 25 and also in the dies to be described. Shedderpunch is typically of generally similar form, with the cylindrical shanksection 31, working in the bearing block 32 with bushing 33, and thehobbed working section 34 conforming at least approximately to thefinished gear and guided by punch guide 35. The bearing blocks and punchguides, as well as the dies and other members to be described, arefixedly mounted in coaxial alinement in any suitable manner, for examplewithin a rigid rectangular frame or box, not explicitly shown, withinwhich they fit closely. Such parts may be axially spaced from each otherby spacing blocks such as 26 and 36. Further details of typical mountingand operating mechanism will be found in our prior patent, identifiedabove.

The working dies are coaxially mounted between punch guides 25 and 35,together With spacing plates which may perform additional functions. Inthe present embodiment, four successive cutting dies are shown at 40,distinguished by the numerals A, B, C and D. The single finishing die isshown at 50. Adjacent dies are mutually spaced by the spacing plates 42of inverted U-form. Vertical channels 44 in the upper portions of thespacing plates form coolant nozzles for directing oil downward to coolthe dies and carry off chips through the passages formed between thevertical legs of the spacing plates. Oil under pressure is supplied topassages 44 during the working stroke of the machine via the conduit 52and distributing chamber 54.

Work blanks 60 are fed to the machine through a vertical feed track 64,the lower part of which is formed by a channel 65 in punch guide 25 andfront face of the transfer hole plate 66. The latter plate also servesto space the first die 40A from the feed track and from punch guide 25,and is channeled on its rearward face to form a chip clearing passage 67and oil nozzle 68 for clearing chips from the front face of the firstdie. Detailed construction and operation of the mechanism for feedingand positioning the blanks may be conventional and need not be describedhere. A channel 63 in punch guide 25 permits visual checking of theblank positions, especially during set-up.

For clarity of illustration, both punches 20 and 30 are shown in FIG. 1in their fully retracted positions. In typical operation of the machine,shedder punch 30 moves to the right, as seen in FIG. 1, and the taperedpilot pin 38 projecting coaxially from its working face 39 picks up thecentral aperture 61 of a blank 60 in track 64. Pusher punch 20 advancesto the left until its working face 29 engages the blank, pressing itfirmly onto the pilot pin 38, which is received in the fitting bore 29in the pusher punch. The blank is thereby held essentially rigidlybetween the two mutually alined punches in accurately centered positionwith respect to the blank aperture.

The work stroke is effected by essentially positive forward movement ofpusher punch 20, to the left as seen in FIG. 1, against a yielding forcemaintained by shedder punch 30. The blank is thereby moved smoothlythrough the successive die apertures. Cutting edges at the peripheriesof those apertures progressively form gear teeth on the blank periphery.The cutting dies 40 shave the gear to within a few thousandths of aninch of the desired form, and the remainder is shaved off as the gearpasses through the final or finish die 50. About one to two thousandthsis typically left on the sides of the gear teeth to be removed by thefinal die, about two to four thousandths at the roots of the teeth, andessentially zero at the tops of the teeth.

After passing through the finish die, the forward movement of the gearis checked by two depending arms 72 of the stripper plate 70, which alsoserves as spacer between the final die and shedder punch guide 35. Thestripper arms are laterally spaced by less than the diameter of thegear, and clearance for them is provided by flatted side areas of theshedder punch, indicated at 73. The shedder punch is then retracted tothe position shown, withdrawing pin 38 from the gear aperture, and thepusher punch is withdrawn to the position shown, ready for another cycleof operation. The finished gear is thereby released, and may be sweptdownward to a storage bin by a blast of oil from the conduit 74 and thenozzle 75. That method of delivering the finished gear is merelyillustrative, and may be considered an alternative to the deliverysystem described in my above identified patent.

In accordance with one aspect of the present invention, finishing diecomprises the die element 76 of relatively thin annular or sleeve form,mounted in the die holder or block 78, which has the same outsidedimensions as cutting dies 4-9. Die insert 76 is provided with die teeth77 on its inner face, and its outer surface 79 is conically tapered andis received in a matching tapered hole in the die block. That diestructure facilitates production of finishing die teeth 77 that fit theexternal flutes on pusher punch 25 with maximum practicable precision,not only along the sides of the respective teeth but also at the topsand roots of the teeth. Such fit insures clean gear surfaces, smooth andaccurate over the entire thickness of the stock.

FIG. 2 shows an illustrative finishing die insert element 76. Theincluded conical angle 6' of external mounting surface 79 is somewhatexaggerated for clarity of illustration. The wall thickness of insert 76is selected, with regard to the material and conical angle, so that theinsert can be pressed into the conical hole in the die holder to shrinkthe die without requiring excessive force and without expanding the dieholder. For an insert of tool steel the wall thickness is typicallyabout 0.025 inch at the smaller end of the die, measured from the rootof the teeth in the die to the outside surface '79. The conical anglemust be small enough to prevent the die insert from popping out of thedie holder, and at the same time must be large enough to keep the insertfrom being pressed further into the die holder by the resistance of theshaving process while the tools are working. We have found that both ofthose conditions can be met effectively if the included angle 0 iswithin the range between about 3 and about The range between about 4 andabout 8 is preferred, and the value of 6 is particularly convenient,since it produces a ratio of 10 to 1 between the axial distance theinsert is pressed into the holder and the resulting reduction of the diediameter.

The outer dimensions of the die element are initially made large enough,as indicated at 100, to provide an effectively rigid unit duringbreaching or other rough forming of the internal die teeth 77. Thatexcess material is then removed and the die element is pressed lightlyinto its mounting block 78, ready for lapping. Initial lapping is donefrom the back of the die with a lap having a slight taper, typicallyabout 0.003 inch in the 4 inches of its length. The outer diameter ofthe die aperture is preferably first brought to a value that exceedsthat of the pushing punch by one or two thousands of an inch, while thedie teeth are still wide enough to prevent free entrance of the pushingpunch. As soon as that punch will go in without producing a press fit,the punch and die are ready to be lapped together. The punch is workedin the die in as many places as there are teeth on the punch, using veryfine diamond lapping compound. After the punch is free in all places,the die is removed from the lapping machine and the die insert ispressed one or two thousands of an inch farther into the die holder.This shrinks the diameter of the die, bringing the die teeth slightlycloser together. The die and punch are then lapped again. This isrepeated until the clearance on the top of the teeth is gone, preferablyleading to a fit on the entire periphery of the teeth within 0.0001 or0.0002. The surfaces of the final die assembly are then preferablyground to remove any part of the insert that protrudes beyond thesurface on either side of the die holder and to aline the edge faces ofthe holder with the die aperture.

FIG. 3 shows preferred illustrative shapes of the respective cuttingedges of the several cutting dies in accordance with a further aspect ofthe present invention. The figure may be considered a view looking inthe direction of the working stroke of the machine from a point justahead of the first cutting die 453A. The view is greatly enlarged andshows one tooth of each die in full and a portion of the adjacent tooth.Those die teeth are denoted by the numeral $0 followed by letters toindicate the respective dies. The sides of the respective die teeth aredenoted by the numeral 82 and the roots of the teeth by the numeral 84,with similar letters to distinguish the different dies. The letter Erefers to finishing die 50 with teeth 77. It will be noted that thesides 82 of some of the successive die teeth are partially superposed,and also the root surfaces 84, or the bottoms of the channels betweenthe die teeth, are mainly superposed. The tops of the cutting die teethare indicated at 86 with distinguishing letters, and are all spacedradially from each other by distances that are approximately, althoughnot exactly, equal.

The actual removal of material from the blank is done primarily by theedges 86 at the tops of the cutting teeth. Those edges are typicallycircular about axis 13. For clarity of illustration, the areas of blank60 that are removed by the respective cutting dies are shaded in dotdashlines, which are not to be confused with conventional shading to denotea section through an element. It will be seen that the primary cuttingis shared approximately equally between all of the cutting dies. Thus,for any given number of dies, the depth of cut of each die can be heldto a minimum.

The form of the final gear is determined by that of finishing die 50,shown in FIG. 3 with root edges at 84E corresponding to the tops of thegear teeth, side edges 82E corresponding to the sides of the gear teeth,and tops 85E corresponding to the gear teeth roots. The outer geardiameter, at MB, is spaced inside the initial periphery of the blanks d0by a distance indicated at fit}. In accordance with one aspect of thepresent invention, that periphery is first cut back toward 84E by thesecond cutting die rather than by the first; and the root edges of thesecond and all subsequent dies, preferably including also the finishingdie, have their root edges at the same diameter. The first cutitng die,on the other hand, has a root edge at 84A, spaced outside of the blankperiphery by an appreciable clearance distance indicated at 92 in FIG.2. That clearance 92 insures that the first cutting die cannot produce achip of ring form. The areas 91 cut by its respective teeth 80A arepositively separated circumferentially by the regions 93 that are leftundisturbed.

The regions 93 of the blank are removed by the second die, with rootedge at 84B. Also, the teeth 80B of the second die deepen the channelsbetween the gear teeth, which were started by the teeth 80A of the firstdie. In order to permit the second die to accomplish both of those cutswithout formation of rings, die teeth 80B are narrower than the teeth ofall the other dies, having side edges at 82B that are set back by adistance indicated at 94 from the common line of the tooth sides of theother cutting dies. That clearance 94 positively produces dead spots inthe cutting action of the second die at both sides of every tooth,indicated at 95. Hence the chips are kept small. Those chips are of twotypes, corresponding to the areas 93 between the initial blank peripheryand the tops of the gear teeth as finally formed; and the areas 95 whichdeepen the channels 91 already cut by the first die between the gearteeth. That deepening action extends almost the full width of thechannels, and contributes significantly toward the total work of gearformation.

A further aspect of the invention provides a convenient and effectivemethod of producing a set of dies and cooperating elements having thedescribed characteristics. In making the dies and punch guides, a pilothole is first formed and is then shaped approximately to the desiredform and size, typically by broaching or by electrical dischargemachining. After suitable heat treatment, which norm-ally precedes suchmachining or follows breaching, the dies are lapped to proper size andtooth form by a special lapping process. A brass lap of the order offour inches long is bobbed with about two to three thousandths of aninch taper, and with the pilot end of the lap just small enough to enterthe die that is to 'be lapped. All dies are lapped from the back side,thereby creating a slight taper from the back. The punch guides arelapped alternately from both sides, producing a slight bell-mouthedcondition.

An illustrative lapping machine is shown somewhat schematically in FIGS.4 and 5. The spindle 104 carries the lap 106 by means of a chuck of anysuitable type and is freely rotatably mounted in the quill 108 inaxially defined position. Quill 108 is vertically movable in the machineframe 110 by means of a rack and pinion, as by the manual handle 109,much in the manner of a drill press quill. Automatic mechanism ispreferably provided for reciprocating the quill, with such factors asspeed of lap travel, power and length of stroke all adjustable. Suchmechanism may employ, for example, a double-acting pneumatic cylinderwith a four-way valve control and variable pressure air supply. Such acylinder may be consideredto be incorporated in quill 103 of FIG. 4,moving the spindle up and down relative to the quill and thussupplementing the action obtainable with handle 109. The die 112 to belapped in held down on the horizontal table 114 by a releasable clamp116 which facilitates accurate placement of the die and permits itsrotation to receive the lap in different positions.

A wet diamond compound of suitable grade is used for lapping. As the diematerial is worn away, the lap is fed down deeper into the die by thehandle 109 until the part of the lap that is the right diameter hasentered the die or punch guide. The lap is frequently withdrawn from thedie, rotated a tooth or two and re-entered to insure uniformity of allteeth.

In accordance with the preferred procedure of the present invention,such lapping is carried out initially by a lap having teeth somewhatthinner than corresponds to the desired tooth form of the die or punchguide until the work has been brought to the proper outer orrootdiameter. The sides of the teeth are then further lapped withoutenlarging the outer diameter of the work. That is accomplished byapplying a light yielding torque to the lap as it is reciprooated in thework. Such torque may conveniently be applied by mounting a torque arm120 on the upper end of quill 108 above the machine frame, preferably bymeans of a friction clutch structure that permits convenient manualadjustment of the orientation of the arm but holds it effectively lockedin the set orientation. A shorter spindle .arm 122 is fixedly mounted onthe upper end of the spindle. A tension spring 124 is mounted betweenthe end of spindle arm 122 and a suitable bracket at a larger radius ontorque arm 120, thereby tending to rotate the spindle into position withthetwo arms alined. Since rotation of the lap is prevented by itsengagement in the teeth of the work, a yielding torque may be appliedbetween the lap and the work in either direction and of convenientlyvariable magnitude by rotating the torque arm to a sutaible angle withrespect to the spindle arm. Such torque applies pressure to one side ofthe teeth all the way around the work. The direction of torque and theposition of the lap in the work are altered frequently to obtainsymmetry and uniformity of tooth form.

Progress of the lapping of a die or punch guide can be convenientlychecked by using the completed pushing punch as a plug gage. Use of thatpunch as the final lap in fitting the insert of the final die hasalready been described. In finishing the cutting die, the desired toothform, as already pointed out in connection with FIG. 3, is suchthat theroots 84 of the die teeth fit the tops of the teeth on the pusher punchaccurately, and that the sides 82 of the die teeth and the tops 86D ofthe teeth of the last cutting die clear the corresponding surfaces ofthe pusher punch by a small amount, typically one or two thousandths ofan inch, which will be removed by the final die. That clearance ischecked during lapping of the cutting dies by inserting the punch in thedie and measuring the rotary play in any suitable manner.

In preparing a set of cutting dies, they are preferably all rough cut tothe same tooth form. The teeth of the first cutting die are first groundoil to produce the concentric cutting edges indicated at 86A in FIG. 3,and that die is then lapped to deepen the channels between the teeth tothe outer diameter indicated at 84A, spaced outside the periphery of thegear blank 60, and to shape the sides of the teeth as at 82A.

All the cutting dies other than the first are preferably lapped beforegrinding. That lapping first brings the outer diameter to the commonsurface shown at 84B, C and D in FIG. 3 by use of a lap with suitablythin teeth. The sides of the teeth are then shaped to provide thedesired clearance. The sides of the teeth of the second die are lappedback further than the others by one or two thousandths to provide theclearance 94 to avoid chips of ring form as already discussed. Thatlatter lapping, and preferably also the shaping of the sides of theteeth of the other cutting dies, is accomplished by torsion lapping,which permits modification of the sides of the teeth without disturbingthe root diameter that has already been established. Finally, aftercompletion of the described lapping, the teeth of the cutting dies otherthan the first are ground back to the desired stepped radii, showntypically at 868, C and D in FIG. 3.

The described procedure is thus capable of producing a set of dies whichwork effectively together to shave a gear with maximum efficiency andprecision. Each die shares significantly and approximately equally inthe work of removing material from the gear blank, and with positiveavoidance of ring chips. Moreover, the accurate uniformity of rootdiameter among all the cutting dies except the first insures precisecentering of the pushing punch and the work as they move through theseries of cutting dies and enter the final die.

I claim: 1. A machine for broaching a circular blank to form a gear,said machine comprising in combination a series of ordered, axiallyalined, apertured dies with cutting edges at the peripheries of theapertures,

means for axially moving a blank successively through the apertures ofthe respective dies to progressively form gear teeth at the blankperiphery to produce a gear, the initial diameter of the blank exceedingthe outer diameter of the formed gear, the first die havingcircumferentially spaced cutting teeth adapted to cut channels ofpredetermined width in the periphery of the blank between the gearteeth, and having an aperture diameter between said cutting teeth thatexceeds said initial diameter of the blank, and the second die having anaperture that clears the sides of said channels in the blank and havingfirst cutting edges adapted to deepen said blank channels and secondcutting edges adapted to form the tops of the gear teeth tosubstantially their final shapes. 2. A machine for broaching a circularblank to form a gear, said machine comprising in combination a series ofordered, axially alined, apertured dies with cutting edges at theperipheries of the apertures,

means for axially moving a blank successively through the apertures ofthe respective dies to progressively form gear teeth at the blankperiphery to produce a gear, the initial diameter of the blank exceedingthe outer diameter of the formed gear,

the first die having circumferentially spaced cutting teeth adapted tocut channels of predetermined width in the periphery of the blankbetween the gear teeth, and having an aperture diameter between saidcutting teeth that exceeds said initial diameter of the blank, and asubsequent die having cutting edges adapted to form the tops of the gearteeth and to clear at least a portion of the boundary of each said blankchannel.

3. A machine for broaching a circular blank to form a gear, said machinecomprising in combination a series of ordered, axially alined, apertureddies with cutting edges at the peripheries of the apertures, an axiallyalined punch having a transverse working face that accurately fits theaperture of the final die,

means for supporting in axial alinement upon the working face of thepunch a circular blank having an initial diameter that exceeds the outerdiameter of the aperture in the final die,

means for moving the punch in a forward working stroke to advance theworking face and the blank successively through the dies other than thefinal die and at least into the final die to progressively form gearteeth at the blank periphery to form a gear, the first die havingcircumferentially spaced cutting teeth adapted to cut channels ofpredetermined width in the periphery of the blank between the gear teethand having an aperture diameter between said cutting teeth that exceedssaid initial diameter of the blank, the second die having first cuttingedges adapted to deepen said blank channels and second cutting edgesadapted to form the tops of the gear teeth to substantially their finalshapes, said first and second cutting edges being mutually spaced byportions of the aperture periphery that clear the sides of said channelsformed by the first die,

the dies after the second die having circumferentially spaced teethseparated by guide surfaces that positively guide the punch in itsmovement toward the final die.

4. A machine for broaching a circular blank to form a gear, said machinecomprising in combination a series of ordered, axially alined, apertureddies with cutting edges at the peripheries of the apertures,

an axially alined punch having a transverse working face that accuratelyfits the aperture of the final die,

means for supporting in axial alinement upon the Working face of thepunch a circular blank having an initial diameter that exceeds the outerdiameter of the aperture in the final die,

means for moving the punch in a forward working stroke to advance theworking face and the blank successively through the dies other than thefinal dies and at least into the final die to progressively form gearteeth at the blank periphery to form a gear,

said final die comprising an annular die element having die teeth on itsinner periphery and having a conically tapered outer periphery, and aconically apertured support in which the die element is mounted,

the included conical angle of the die element outer periphery and of thesupport aperture having a common value such that friction between thesupport and the mounted die element prevents relative forward movementof the die element during said working stroke of the punch and blank andalso prevents relative rearward movement of the die element in absenceof said working stroke.

5. A machine as defined in claim 4, and wherein said conical angles havevalues that are substantially equal and are between about four and abouteight degrees.

6. A machine as defined in claim 4, and wherein the common value of saidconical angles is approximately six degrees.

7. A die having an aperture in the shape of a desired gear periphery andaccurately fitting a punch, said die comprising an annular die elementhaving die teeth on its inner periphery and having a conically taperedouter periphery,

and a conically apertured support in which the die element is coaXiallymounted,

the included conical angle of the die element outer periphery and of thesupport aperture having a common value such that friction between thesupport and the mounted die element prevents relative forward movementof the die element during said working stroke of the punch and blank andalso prevents relative rearward movement of the die element in absenceof said working stroke.

References Cited by the Examiner UNITED STATES PATENTS 2,392,747 1/ 1946La Pointe -63 3,022,710 2/1962 Kopec 2995 .1 3,057,264 10/ 1962 Musser90-63 3,080,776 3/ 1963 Muenchinger 76107 3,111,865 11/1963 Wildhaber76101 3,194,090 7/1965 Becker 76-107 WILLIAM W. DYER, JR., PrimaryExaminer.

G. A. DOST, Assistant Examiner,

1. A MACHINE FOR BROACHING A CIRCULAR BLANK TO FORM A GEAR, SAID MACHINECOMPRISING IN COMBINATION A SERIES OF ORDERED, AXIALLY ALINED, APERTUREDDIES WITH CUTTING EDGES AT THE PERIPHERIES OF THE APERTURES, MEANS FORAXIALLY MOVING A BLANK SUCCESSIVELY THROUGH THE APERTURES OF THERESPECTIVE DIES TO PROGRESSIVELY FORM GEAR TEETH AT THE BLANK PERIPHERYTO PRODUCE A GEAR, THE INITIAL DIAMETER OF THE BLANK EXCEEDING THE OUTERDIAMETER OF THE FORMED GEAR, THE FIRST DIE HAVING CIRCUMFERENTIALLYSPACED CUTTING TEETH ADAPTED TO CUT CHANNELS OF PREDETERMINED WIDTH INTHE PERIPHERY OF THE BLANK BETWEEN THE GEAR TEETH, AND HAVING ANAPERTURE DIAMETER BETWEEN SAID CUTTING TEETH THAT EXCEEDS SAID INITIALDIAMETER OF THE BLANK, AND THE SECOND DIE HAVING AN APERTURE THAT CLEARSTHE SIDES OF SAID CHANNELS IN THE BLANK AND HAVING FIRST CUTTING EDGESADAPTED TO DEEPEN SAID BLANK CHANNELS AND SECOND CUTTING EDGES ADAPTEDTO FORM THE TOPS OF THE GEAR TEETH TO SUBSTANTIALLY THEIR FINAL SHAPES.